A conventional automatic transmission used in vehicles generally includes a multi-stage gear mechanism, a torque converter connected thereto, and a plurality of clutch elements actuated by hydraulic pressure for selecting one of the gears of the gear mechanism. An electronic hydraulic control system for an automatic transmission operates by selectively supplying hydraulic pressure from a hydraulic pump to the clutch elements by a plurality of control valves such that shifting may be realized automatically according to the driving situation.
The hydraulic control system generally includes a hydraulic fluid source, a line pressure controller for regulating hydraulic pressure supplied from the fluid source to line pressure, and a hydraulic pressure distributor for determining a hydraulic flow path corresponding to the respective transmission speeds according to the hydraulic pressure from the shift controller and suitably distributing the operational pressure to each friction element.
When a user desires to change the gear selection in the vehicle, for example from Drive to Park or Drive to Neutral, the flow of hydraulic fluid to one or more clutch mechanisms is either enabled or interrupted depending on the particular gear selected. In current designs the flow, or interruption of flow, of fluid and consequently the engagement or disengagement of these clutches, can be abrupt. The rapid change of states within the transmission can result in a clunky or bumpy feeling in the transmission when the transmission can result in a clunky or bumpy feeling in the transmission when the transmission is shifted from a drive gear to either Neutral or Park, as energy that had previously been stored in the driveline in rapidly released. As users may perceive this feeling as a defect or poor design in the transmission, it is desirable to reduce this sensation as much as possible.
Therefore, it is desirable to provide an automatic transmission with the ability to smoothly transition between gears, particularly between the Drive and Neutral and Drive and Park gears.